Method and apparatus for manually selecting battery charging process

ABSTRACT

A method for charging a rechargeable battery pack includes providing a charger having first and second charging processes, and manually selecting one of the first and second charging processes. The charging method may include a step for indicating status or end of the selected one charging process. The first charging process may include the steps of providing a fast charging current, indicating end of the fast charging current and providing an equalization current. The second charging process may include the steps of providing a fast charging current, subsequently providing an equalization current and indicating end of equalization current. The second charging process may also include a temperature checking step. Further disclosed is a battery charging apparatus including a charger for charging a battery and having first and second charging processes, and a switch connected to the charger for manually selecting one of the first and second charging processes. The charger may include a microprocessor. Further, the apparatus may include a display output and/or sound output connected to the charger. The display output and/or sound output may indicate status or end of the selected one charging process. The display output may comprise a light bulb, a light emitting diode and/or a liquid crystal display. The sound output may comprise a speaker and/or a piezo-electric device.

FIELD OF THE INVENTION

This invention relates generally to a method and apparatus for chargingrechargeable batteries.

BACKGROUND OF THE INVENTION

The battery packs for portable power tools, outdoor tools, and certainkitchen and domestic appliances usually have several cells disposed inseries. Users typically remove the battery packs from the batterycharger after completion of the fast charging process, but beforesufficient equalizing charge has been provided to the battery forequalizing the capacities of the various cells. Over time, the cellcapacities become further out of balance, with some cells becomingsignificantly lower in capacity relative to the others.

The battery pack is typically usable until the charge in thelower-capacity cells is depleted. Accordingly, the user perceives thatthe capacity of the battery pack and/or battery life is decreased andmay incorrectly attribute this to a "memory" problem. The user may alsoperceive that the battery pack may be defective.

It is preferable to provide a method and apparatus that enables the userto equalize, or "refresh," the cell capacities, in order to restorebattery pack capacity.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method for charging arechargeable battery pack is proposed. The charging method includesproviding a charger having first and second charging processes, andmanually selecting one of the first and second charging processes. Thecharging method may include a step for indicating status or end of theselected one charging process. The first charging process may includethe steps of providing a fast charging current, indicating end of thefast charging current and providing an equalization current. The secondcharging process may include the steps of providing a fast chargingcurrent, subsequently providing an equalization current and indicatingend of equalization current. The first or second charging processes mayalso include a temperature checking step.

Also disclosed herein is a battery charging apparatus comprising acharger for charging a battery and having first and second chargingprocesses, and a switch connected to the charger for manually selectingone of the first and second charging processes. The charger may includea microprocessor. Further, the apparatus may include a display outputand/or sound output connected to the charger. The display output and/orsound output may indicate status or end of the selected one chargingprocess. The display output may comprise a light bulb, a light emittingdiode and/or a liquid crystal display. The sound output may comprise aspeaker and/or a piezo-electric device.

Additional features and benefits of the present invention are described,and will be apparent from, the accompanying drawings and the detaileddescription below.

BRIEF DESCRIPTION OF THE INVENTION

The accompanying drawings illustrate preferred embodiments of theinvention according to the practical application of the principlesthereof and in which:

FIG. 1 is a circuit schematic diagram of a battery charger according tothe present invention; and

FIG. 2 is a flowchart illustrating the charging process according to thepresent invention.

DETAILED DESCRIPTION

The invention is now described with reference to the accompanyingfigures, wherein like numerals designate like parts. All the teachingsof the Saar U.S. Pat. Nos. 4,388,582 and 4,392,101 are herebyincorporated by reference into this specification.

Referring to FIG. 1, a battery 10 is connected to a charger controlcircuit 20. Battery 10 comprises a plurality of battery cells 11connected in series, which dictate the voltage and storage capacity forbattery 10. Battery 10 includes three battery charging contacts: firstbattery contact 12, second battery contact 13, and third battery contact14. Battery contact 12 is the B+ (positive) terminal for battery 10.Battery contact 13 is the B- or negative/common terminal. Batterycontact 14 is the S or sensing terminal. Battery contacts 12 and 13receive the charging current sent from the charger control circuit 20(preferably from current source 22, as discussed below)for charging thebattery 10.

As shown in FIG. 1, the battery cells 11 are coupled between the batterycontacts 12 and 13. In addition, preferably coupled between batterycontacts 13 and 14 is a temperature sensing device 15, such as anegative temperature co-efficient (NTC) resistor, or thermistor, R_(T).The temperature sensing device is preferably in closer proximity to thecells 11 for monitoring of the battery temperature. Persons skilled inthe art will recognize that other components, such as capacitors, etc.,or circuits can be used to provide a signal representative of thebattery temperature.

The charger control circuit 20 includes positive terminal (B+) 16 andnegative (B-) terminal 17, which are coupled to battery 10 via batterycontacts 12 and 13, respectively. The positive terminal may also act asan analog/digital input A/DINPUT_(v), in order for the charger controlcircuit 20 to detect the battery voltage. In addition, the chargercontrol circuit 20 may include an analog/digital input A/DINPUT_(T),which is coupled to the temperature sensing device 15 via the thirdbattery contact 14 (S). This allows the charger control circuit 20 tomonitor the battery temperature. Charger control circuit 20 includes amicroprocessor 21 for controlling the charging and monitoringoperations. Charger control circuit 20 may control a current source 22that provides current to battery 10. This current may be a fast chargingcurrent and/or an equalization current. Current source 22 may beintegrated within charger control circuit 20.

Switch S1 is connected to charger control circuit 20 via switch inputSWIN. Switch S1 will be used to select the desired charging mode, orcharging process, as discussed below.

Sound output circuit 30 may be connected to charger control circuit 20via sound output SOUT. Circuit 30 may include a speaker 31 and/orpiezo-electric device 32. Circuit 30 will emit an audio signal forindicating status and/or end of the charging processes, as discussedbelow. Persons skilled in the art will recognize that circuit 30 mayalso be integrated within charger control circuit 20.

Similarly, display output circuit 40 may be connected to charger controlcircuit 20 via display output DOUT. Circuit 40 may include a liquidcrystal display (LCD) 41, a light bulb 42 and/or a light emitting diode(LED) 43. Circuit 40 will emit a visual signal for indicating statusand/or end of the charging processes, as discussed below. Persons sidledin the art will recognize that circuit 40 may also be integrated withincharger control circuit 20.

FIG. 2 is a flowchart of the different steps comprised in the proposedmethod. The first step (ST1) is to begin the charging process. Thecharger control circuit 20 checks the status of switch SW1 to determinewhich charging mode or process to use (ST2). In the present embodiment,the user may select between a fast charging process and a "refresh"process for equalizing the battery cells.

Persons skilled in the art will recognize that this checking step ST2may be periodically conducted throughout the entire process shown inFIG. 2, allowing the user to select and change the charging process atany time during the proposed method. Accordingly, in the presentembodiment, the user may be able to select between a fast chargingprocess and a refresh process at any time during the proposed method.

Assuming the user selects the fast charging process, the charger controlcircuit 20, via its A/D inputs, may sense the battery temperature T(ST3). The charger control circuit 20 preferably continues to sense thebattery temperature until it is below a predetermined temperature X(ST4). Preferably, the predetermined temperature X for NiCd batteries isbetween about 45° and 65° Celsius, with the preferred temperature beingabout 55° Celsius. This preferred temperature has been selected as acompromise between the battery cooling time, which increases the timerequired for charging the battery pack and the battery charge acceptancecharacteristics.

When the battery temperature is below X, the charger control circuit 20sends a fast charging current into the battery, in order to recharge thebattery (ST5). The charger control circuit 20 may then monitor differentbattery parameters, including current, voltage and temperature of thebattery, to terminate the fast charging current (ST6).

Persons skilled in the art will recognize that any voltage monitoringmethods, including the Saar double inflection termination methoddescribed in U.S. Pat. Nos. 4,388,582 and 4,392,101, theminus-delta-voltage method, the peak detect method, and/or the voltageslope detect method may be used to terminate the fast charging current.Similarly, persons skilled in the art will recognize that temperaturemonitoring methods, including the absolute temperature terminationmethod and/or the temperature change rate termination method may be usedto terminate the fast charging current.

Upon termination of the fast charging current, circuits 30 and/or 40 mayindicate the end of the fast charging process (ST7). Accordingly, asound signal may be emitted by speaker 31 and/or piezo-electric device32. Similarly, a visual signal may be emitted by a liquid crystaldisplay (LCD) 41, a light bulb 42 and/or a light emitting diode (LED)43. Preferably, a visual signal is emitted by the LED 43.

Simultaneously or soon thereafter, a small equalization current isapplied to battery 10 (ST8). Charger control circuit 20 preferably willcontinue to apply the equalization current until the battery 10 isdisconnected or until a predetermined time period has elapsed (ST9).Preferably the time period is between four and eight hours. Afterwards,the charging process is complete (ST10).

Assuming the user selects the refresh mode, the charger control circuit20, via its A/D inputs, may sense the battery temperature T (ST11). Thecharger control circuit 20 preferably continues to sense the batterytemperature until it is below a predetermined temperature Y (ST12).Preferably, the predetermined temperature Y is below or around the lowerend of the range for predetermined temperature X. Accordingly, thepreferred temperature for predetermined temperature Y is about 45°Celsius for NiCd batteries. This temperature has been selected toincrease the charge acceptance of the battery, at the expense of waitingtime.

Alternatively, the charger control circuit 20 may suspend the chargingprocess until a predetermined period of time has elapsed (ST18).Preferably, this period of time is about 2 hours.

When the battery temperature is below Y or after the predeterminedperiod of time has elapsed, the charger control circuit 20 preferablysends a current into the battery. Preferably, the charger controlcircuit 20 sends a fast charging current into the battery 10 (ST13), asexplained above. However, persons skilled in the art will recognize thatthe circuit 20 may send any other current into the battery 10, whenimplementing the present invention. The charger control circuit 20 maythen monitor the different battery parameters, including current,voltage and temperature of the battery, to terminate the fast chargingcurrent (ST14), as explained above.

After the fast charging current is terminated, a small equalizationcurrent may be applied to battery 10 (ST15). Charger control circuit 20will preferably continue to apply the equalization current until thebattery 10 is disconnected or until a predetermined time period haselapsed (ST16). Preferably the time period is between four and eighthours.

When the predetermined time period has elapsed, circuits 30 and/or 40may indicate the end of the refresh mode (ST17). Accordingly, a soundsignal may be emitted by speaker 31 and/or piezo-electric device 32.Similarly, a visual signal may be emitted by a liquid crystal display(LCD) 41, a light bulb 42 and/or a light emitting diode (LED) 43.Afterwards, the charging process is complete (ST10).

Persons skilled in the art may recognize that the battery pack 10 is notwholly discharged and then charged during the refresh mode in thepreferred embodiment.

Persons skilled in the art may recognize other alternatives or additionsto the means or steps disclosed herein. However, all these additionsand/or alterations are considered to be equivalents of the presentinvention.

What is claimed is:
 1. A battery charging apparatus comprising:a chargerfor charging a battery and having a first and second charging processes;and a switch connected to the charger for manually selecting between thefirst and second charging processes, wherein the first charging processis a fast charging process and the second charging process is anequalization process.
 2. The apparatus of claim 1, wherein the chargercomprises a microprocessor.
 3. The apparatus of claim 1, furthercomprising a display output connected to the charger.
 4. The apparatusof claim 3, wherein the display output comprises at least one of thegroup comprising a light emitting diode, a liquid crystal display and alight bulb.
 5. The apparatus of claim 3, wherein the display outputindicates status of a selected charging process.
 6. The apparatus ofclaim 3, wherein the display output indicates end of a selected chargingprocess.
 7. The apparatus of claim 1, further comprising a sound outputconnected to the charger.
 8. The apparatus of claim 7, wherein the soundoutput comprises at least one of the group comprising a speaker and apiezo-electric member.
 9. The apparatus of claim 7, wherein the displayoutput indicates status of a selected charging process.
 10. Theapparatus of claim 7, wherein the display output indicates end of aselected charging process.
 11. The apparatus of claim 1, wherein thefirst charging process comprises providing a fast charging current tothe battery, indicating end of fast charging current and providing anequalization current to the battery.
 12. The apparatus of claim 1,wherein the second charging process comprises providing a fast chargingcurrent to the battery, providing an equalization current to the batteryand indicating end of the equalization current.
 13. The apparatus ofclaim 1, wherein the second charging process comprises providing anequalization current to the battery and indicating end of theequalization current.
 14. The apparatus of claim 1, wherein the firstcharging process comprises sensing battery temperature.
 15. Theapparatus of claim 1, wherein the second charging process comprisessensing battery temperature.
 16. The apparatus of claim 1, wherein thesecond charging process equalizes the battery without substantiallydischarging the battery.
 17. A method for charging a batterycomprising:providing a charger having first and second chargingprocesses; and manually switching the charger between first and secondcharging processes, wherein the first charging process is a fastcharging process and the second charging process is an equalizationprocess.
 18. The charging method of claim 17, further comprisingindicating status of a selected charging process.
 19. The chargingmethod of claim 17, further comprising indicating end of a selectedcharging process.
 20. The charging method of claim 17, wherein the firstcharging process comprises providing a fast charging current, indicatingend of the fast charging current and providing an equalization current.21. The charging method of claim 20, wherein the first charging processcomprises sensing battery temperature.
 22. The charging method of claim17, wherein the second charging process comprises providing a fastcharging current to the battery, providing an equalization current tothe battery and indicating end of the equalization current.
 23. Thecharging method of claim 22, wherein the second charging processcomprises sensing battery temperature.
 24. The charging method of claim17, wherein the second charging process comprises providing anequalization current to the battery and indicating end of theequalization current.
 25. The charging method of claim 17, wherein thesecond charging process equalizes the battery without substantiallydischarging the battery.
 26. A battery charging apparatus comprising:acharger for charging a battery and having a fast charging process and arefresh process; and a switch connected to the charger for manuallyselecting between the fast charging and refresh processes; wherein thefast charging process comprises providing a fast charging current to thebattery, indicating end of fast charging current and providing anequalization current to the battery, and the refresh process comprisesproviding an equalization current to the battery and indicating end ofthe equalization current.
 27. The apparatus of claim 26, wherein thecharger comprises a microprocessor.
 28. The apparatus of claim 26,further comprising a display output connected to the charger.
 29. Theapparatus of claim 28, wherein the display output comprises at least oneof the group comprising a light emitting diode, a liquid crystal displayand a light bulb.
 30. The apparatus of claim 28, wherein the displayoutput indicates end of fast charging current or equalization current.31. The apparatus of claim 26, wherein the refresh process comprisessensing battery temperature.
 32. The apparatus of claim 26, wherein therefresh process comprises suspending current sent to the battery until apredetermined period of time has elapsed.
 33. The apparatus of claim 26,wherein the refresh process comprises providing a fast charging currentto the battery.
 34. The apparatus of claim 26, wherein the refreshprocess equalizes the battery without substantially discharging thebattery.
 35. A method for charging a battery comprising:providing acharger having fast charging and refresh processes; and manuallyswitching the charger between the fast charging and refresh processes;wherein the fast charging process comprises providing a fast chargingcurrent to the battery, indicating end of fast charging current andproviding an equalization current to the battery, and the refreshprocess comprises providing an equalization current to the battery andindicating end of the equalization current.
 36. The charging method ofclaim 35, wherein the refresh process comprises sensing batterytemperature.
 37. The charging process of claim 35, wherein the refreshprocess comprises suspending current sent to the battery until apredetermined period of time has elapsed.
 38. The charging process ofclaim 35, wherein the refresh process comprises providing a fastcharging current to the battery.